Field of the Invention
The present invention relates to a toner used in a recording method such as electrophotography.
Description of the Related Art
In recent years, electrophotographic devices have been required to demonstrate improved toner low-temperature fixability in order to achieve greater energy savings. Crystalline resins represented by crystalline polyester, which are able to realize both low-temperature fixability and storability, are attracting attention as toner constituent materials. Crystalline resins have a melting point, and in addition to melting rapidly at that melting point, are expected to demonstrate considerable improvement of low-temperature fixability by plasticizing other resins.
For example, Japanese Patent No. 4858165 proposes a toner that contains an amorphous polyester resin, which is synthesized using at least one type of alkyl succinic acid, alkenyl succinic acid and anhydride thereof as an acidic component, and a crystalline polyester resin.
This publication describes that the occurrence of minute melting unevenness during toner melting is inhibited and, even when thermal variation occurs during toner fixing, high-quality color images are obtained without the occurrence of offset and other fixing defects or uneven image gloss values even in regions of high image density by using an aliphatic crystalline polyester resin for the crystalline polyester resin and combining with the use of amorphous polyester resins of different molecular weights having a long-chain alkyl group or alkenyl group.
On the other hand, crystalline resins tend to exhibit inadequate dispersion in toner, and dispersion diameter becomes large or the composition, including other materials, becomes heterogeneous, and as a result thereof, these resins easily cause broadening of charge distribution. Moreover, “fogging”, in which toner is developed in the margin of an image, tends to occur easily, thereby leaving room for improvement.
Toner containing binder resin in the form of crystalline polyester and amorphous polyester, and to which has been added silica particles having fatty acid amide supported on the surface thereof, has been proposed in Japanese Patent Application Laid-open No. 2010-26185, for example, as a technology for improving the dispersibility of crystalline polyester resin.
This publication describes that the use of silica particles having fatty acid amide supported on the surface thereof makes it possible to uniformly crystallize crystalline polyester in toner particles and prevent decreases in toner storage stability, thereby making it possible to prevent the occurrence of toner particle aggregation. However, the addition of inorganic particles in the form of silica particles has the potential to cause a thickening effect. Thus, from the viewpoint of low-temperature fixability, it is necessary to improve the dispersibility of crystalline polyester without relying on inorganic particles.
In addition, Japanese Patent Application Laid-open No. 2006-258963 proposes a toner obtained by carrying out a melting and kneading step using a toner composition comprising a raw material containing a crystalline resin, an amorphous resin and a colorant, and a powder derived from the raw material having a volume-based median particle diameter (D50) of 0.5 μm to 8 μm, followed by going through a cooling step, a pulverizing step, a classifying step and a surface treatment step.
According to this publication, although a toner is obtained that has favorable durability and low-temperature fixability, a plurality of kneading step is substantially required, and there is still room for improvement when considering such factors as productivity.